MIPS汇编中的C数组索引? [英] C array indexing in MIPS assembly?

问题描述

问题:

void swap (int v[], int k)
{
int temp;
temp = v[k];
v[k] = v[k+1];
v[k+1] = temp;
}

我的问题是为什么要在 $ t1 中添加int v [] ?(无论谁都没有评论，所以我假设 $ a0 是 v [] 和 $ a1 是 k).

My question is why does int v[] get added $t1? (whoever did this didn't even comment it so I'm assuming $a0 isv[] and $a1 is k).

答案:

swap: sll $t1, $a1, 2
add $t1, $a0, $t1
lw $t0, 0($t1)
lw $t2, 4($t1)
sw $t2, 0($t1)
sw $t0, 4($t1)
jr $ra

我知道这是用来交换变量的，但是它在做什么，为什么要在 v [] 和 k 之间添加? v [] 是否不是已声明变量的数组，如何将它与整数 k 相加?

I know this is used to swap variables but what is it doing here, why is it adding v[] with k? Isn't v[] a array of declared variables, how can you add it with a integer k?

推荐答案

谁做的甚至都没有评论，所以我假设$ a0是v []而$ a1是k

whoever did this didn't even comment it so I'm assuming $a0 is v[] and $a1 is k

这些是MIPS 呼叫约定.函数的前4个参数位于 $ a0 .. $ a3 中，返回值(此处不需要)位于 $ v0 中(和 $ v1 >(如果需要).返回地址在寄存器 $ ra 中.

These are the MIPS calling conventions. First 4 arguments of a function are in $a0..$a3 and return value (not required here) is in $v0 (and $v1 if required). Return address is in register $ra.

我知道这是用来交换变量的，但是它在做什么，为什么要在v []上加上k?isnt v []一个已声明变量的数组，如何将它与整数k相加?

I know this is used to swap variables but what is it doing here, why is it adding v[] with k? isnt v[] a array of declared variables, how can you add it with a integer k?

v []实际上是一个int数组.保持变量v的是数组的地址.向数组地址添加值是访问数组特定元素的方法.

v[] is indeed an array of int. What holds variable v is the address of the array. Adding a value to an array address is the way to go to specific elements of the array.

swap:                   # void swap (int v[], int k)
                        ; so v[] is in $a0 and k in $a1
      sll $t1, $a1, 2   ; k*=4 (ie sizeof(int))
      add $t1, $a0, $t1 ; $t1=@v+4*k==@(v[k])
      lw $t0, 0($t1)    #   temp = v[k];
      lw $t2, 4($t1)    ; 4(t1) is @(v[k])+4==@(v[k+1]
                        ; $t0==temp==v[k], $t2==v[k+1]
      sw $t2, 0($t1)    #   v[k] = v[k+1]; 
      sw $t0, 4($t1)    #   v[k+1] = temp;
      jr $ra            ; go back to caller

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